They called in big political guns, notably US Representative Stephen F. Lynch, the South Boston Democrat who is running for US Senate, at a noon rally. They even rolled out an inflatable Cerberus, the three-headed dog that guards the gates of the underworld. The private equity firm that owns the hospital’s parent, Steward Health Care System, is named after the mythical creature.

“The dog came out of retirement,” said David Schildmeier, spokesman for the Massachusetts Nurses Association, who said the hellhound’s only previous appearance was at a protest last year outside the New York headquarters of Cerberus Capital Management, which formed the Steward hospital and doctors group in 2010.

Inside the hospital, doctors and administrators said it was largely business as usual — except that they canceled elective surgeries for the day and brought in about 60 replacement nurses. They also hired trucks with billboards proclaiming the union was living in the past. Nurses stood in the street trying to block the trucks and attach their own signs to the vehicles.

“In today’s economy, nurses sitting by empty beds making $52 an hour is not feasible,” said Daniel Knell, who took over in 2011 as president of Quincy Medical Center.

At the end of the day, nothing was resolved. Nurses were set to return to their jobs Friday morning without a contract. And there was no agreement between the two sides on the basic facts of what prompted the unusual one-day strike. While the nurses cited inadequate staffing, management insisted the union was pushing for higher wages and benefits.

The walkout took place against a backdrop of looming cuts in government funding for Medicare and Medicaid, the public insurance programs for older and low-income people.

“There is a lot of pressure being put on the hospitals,” Lynch told more than 200 nurses and their supporters. “The reimbursement rates are not there. They are being put under pressure to reduce costs, and they are looking at making nurses work longer hours with fewer nurses on staff. That’s not the way we need to be going.”

The strike got underway at 6 a.m., when unionized nurses walked out of the
hospital to join nurses from Norwood Hospital, Morton Hospital in Taunton, and other Steward-owned and nonprofit hospitals who came to show their support.

“We need to bring it to the community to support the issues,” said Paula Ryan, a recovery room nurse at Quincy Medical who chairs the union local. “It’s been a long time coming. It’s been a struggle every day, nurses trying to provide the better care.”

Regulators from the state Department of Public Health showed up before dawn to make sure replacement nurses were certified and had been trained by hospital officials. A contingent of Quincy police officers — paid for by Steward — kept watch at the protest. “The financial impact for today alone is exceptional,” Knell said. He warned the hospital could be hurt further if patients chose to go to competing hospitals in Boston, Milton, or Weymouth because of what he said were false charges of safety problems.

“If the community doesn’t support the facility because of the rhetoric, it could do financial damage to us,” Knell said.

Nurses authorized the strike last month after their negotiators failed to reach agreement with Steward on a new contract. Their last contract expired before Steward acquired the bankrupt hospital in October 2011. Through an understanding between labor and management, they have been working under the terms of a separate Steward contract with union nurses at Steward-owned Carney Hospital in Dorchester.

Barry Chin/Globe Staff

A nurse from another Steward hospital waved a sign outside Quincy Medical Center to drum up support.

The union was notified in February that the hospital will close a 40-bed medical surgical floor and lay off 30 nurses who worked there along with 40 technicians, orderlies, and laborers, though the cuts have yet to take effect. Union officials contend that will aggravate already overcrowded conditions, but hospital officials insist there are often empty beds.

Steward and Cerberus executives are more interested in making money from their for-profit community hospitals than caring for patients, union members said. But hospital officials said the Quincy strike was part of a national union effort to inflate wages and keep staffing unnecessarily high at a time when more health care is shifting from in-patient to outpatient services.

“I consider nurses as our colleagues, and I value the work they do for patients,” said Dr. Nissage Cadet, chief of surgery at Quincy Medical Center. “But health care is changing, and that’s the right thing for patients. Steward came in and bailed out a hospital that was about to close in months. The quality of the institution has never been this good.”

On the picket line, however, nurses said conditions have gotten so bad that patients are being “boarded” in the emergency department for long periods while waiting to see a doctor. Department nurse Kathleen LeBretton said such episodes happen two to three times a week.

Hospital officials insisted they only board psychiatric patients in a section of the emergency room while they await transfer to other hospitals because Quincy Medical does not have psychiatric beds.

The nurses were supported by Dr. Robert Noonan, a private practice physician who sometimes works with Quincy Medical Center. “There was a patient last month who was a patient of mine in her 80s,” he said. “The closed surgical floor was full, and she was boarded in the emergency room for 18 hours.”

Hospital officials contended the nurses and their backers were making false claims in an effort to get more money.

“I’ve been a nurse myself,” Knell said. “And when I took my oath to take care of my patients, I meant it. I don’t know that I would ever walk away from the bedside of my patient for financial reasons.”